1. Field of the Invention
The invention relates to a liquid crystal display (LCD) device, and more particularly to an LCD device of in plane switching mode (IPS mode) with an enhanced aperture ratio and an enhanced transmittance, and a method for manufacturing the same.
2. Description of the Related Art
LCD devices have various advantages that they are light in weight, thin in thickness and low in power consumption, as compared to cathode ray tube (CRT) display devices. Therefore, such LCD devices are used in various terminals of information system and video units and the like, as a substitute for the CRT display devices. The LCD device typically adopts TN (Twist Nematic) mode as a LCD driving method. However, the widely utilized TN mode LCD device is disadvantageous in that its viewing angle is narrow. In order to eliminate the problem involved due to such a narrow viewing angle, therefore, plane switching (IPC) mode LCD devices have been proposed.
FIG. 1 shows a plan view of a conventional IPS mode LCD device. Its structure will now be described with reference to FIG. 1.
As shown in FIG. 1, a gate bus line 2 and a data bus line 6 are arranged in such a fashion that they cross each other, to define a unit pixel. A thin film transistor (TFT) 10 as a switching element is disposed near the intersection of the gate bus line 2 and the data bus line 6. As well known, the TFT 10 includes a gate electrode 2a, a channel layer (not shown), and source/drain electrodes 6a and 6b. A counter electrode 4 is also disposed in the unit pixel. The counter electrode 4 comprises a pair of first branches 4a disposed at the both sides of the unit pixel in parallel to the data bus line 6, second branches 4b interposed between the first branches 4a, and a bar 4c functioning as a common electrode line. The bar 4c extends in parallel to the gate bus line 2 while being spaced apart from the gate bus line 2 by a maximum distance in the unit pixel. The bar 4c connects respective one-side ends of the first branches 4a and second branches 4b together. A pixel electrode 8 is also disposed in the unit pixel. The pixel electrode 8 comprises a pair of first electrode parts 8a overlapping with respective first branches 4a of the counter electrode 4, second electrode parts 8b interposed between the second branches 4b of the counter electrode 4, and a third electrode part 8c connecting together respective ends of the first and second electrode parts 8a and 8b arranged near the gate bus line 2 while contacting the source electrode 6a of the TFT 10.
Meanwhile, although not shown, an upper substrate is disposed over the lower substrate having the above-described structure while being spaced apart from the lower substrate by a desired distance. A liquid crystal layer comprising a number of liquid crystal molecules is interposed between the upper substrate and the lower substrate.
FIG. 2 shows a cross-sectional view of the conventional IPS mode LCD device. Referring to FIG. 2, the fabrication of this device will be described.
A certain opaque metal film is deposited on a glass plate 1. The opaque metal film is patterned according to a known photo process, thereby forming a gate bus line (not shown) including a gate electrode 2a, and a counter electrode 4 including first and second branches 4a and 4b and a bar (not shown). A gate insulating film 3 is then deposited over the entire upper surface of the glass plate 1 with the gate bus line and the counter electrode formed. A channel layer 5 is formed on a portion of the gate insulating film 3 covering the gate electrode 2a. A metal film for source/drain is deposited on the channel layer 5 and the exposed portion of the gate insulating film 3. By patterning the metal film for source/drain, a data bus line 6 having a source electrode 6a and a drain electrode 6b is formed. Thus, a TFT 10 is fabricated. An ohmic contact layer (not shown) is interposed between the channel layer 5 and the source/drain electrodes 6a and 6b. 
A protection layer 7 is deposited over the resultant structure obtained after completion of the above process, followed by an etching treatment to expose a part of the protection layer 7. A transparent metal film, such as an ITO film is deposited on the protection layer 7 and patterned to form a pixel electrode 8 having first, second and third electrode parts 8a, 8b, and 8c. The third electrode part 8c of the pixel electrode 8 is arranged to contact the source electrode 6a of the TFT 10.
Such an IPS mode LCD device has a structure in which its counter electrode and its pixel electrode for driving liquid crystals are arranged in parallel to each other on a single substrate. Therefore, an electric field generated between the counter electrode and the pixel electrode is parallel to the main surface of the substrate. Consequently, since the liquid crystal molecules are aligned in such a fashion that their long axis are oriented in parallel to the electric field, users can see the long axes of the liquid crystal molecules in any directions. Thus, the IPS mode LCD device has improved characteristics in terms of the viewing angle, as compared to TN mode LCD device.
However, the above-mentioned conventional IPS mode LCD device fails to satisfactorily improve the aperture ratio and transmittance because the counter electrode and the pixel electrode are formed of opaque metals. Moreover, the IPS mode LCD device can have a desired brightness only at an increased intensity of back light resulting in an increased consumption of electric power.
Therefore, in one aspect of the present invention, it is an object to provide an IPS mode LCD device with an enhanced aperture ratio and an enhanced transmittance.
Further, in another aspect of the present invention, it is an object to provide a method for manufacturing an IPS mode LCD device with an enhanced aperture ratio and an enhanced transmittance.
In accordance with one aspect, the present invention provides an in plane switching mode liquid crystal display device comprising: a transparent insulating substrate; a gate bus line and a data bus line arranged in a cross fashion on the transparent insulating substrate to define a unit pixel area; a common electrode line disposed in parallel to the gate bus line while being spaced at most apart from the gate bus line in the unit pixel area, the common electrode line having a pair of shields respective disposed at both lateral edges of the unit pixel area; a thin film transistor disposed near an intersection of the gate bus line and the data bus line; a counter electrode arranged in the unit pixel area between the shield of the common electrode line and made of a transparent conductor, the counter electrode including a plurality of branches arranged in parallel to the data bus line, and a bar contacting the common electrode line and connecting respective one-side ends of the branches together; and a pixel electrode formed of a transparent conductor and including a pair of first electrode parts respectively overlapping with the shields of the common electrode line while extending in parallel to the data bus line, second electrode parts interposed each between adjacent ones of the branches included in the counter electrode, and a third electrode part contacting a part of the thin film transistor while connecting together respective one-side ends of the first and second electrode parts.
In accordance with another aspect, the present invention provides a method for manufacturing an in plane switching (IPS) mode LCD device comprising steps of: depositing a first opaque metal film over a transparent insulating substrate; patterning the first opaque metal film to form a gate bus line including a gate electrode and a common electrode line disposed in parallel to the gate bus line while being spaced at most apart from the gate bus line in a unit pixel and having a pair of shields disposed at both lateral edges of the unit pixel; forming a gate insulating film on the transparent insulating substrate to cover the gate bus line and the common electrode line; forming a channel layer on the gate insulating part over the gate electrode; forming source/drain electrodes on the channel layer to form a thin film transistor (TFT) and to define a unit pixel, and forming a data bus line to be arranged in a cross fashion with respect to the gate bus line; forming, on a structure obtained after completion of the formation of the source/drain electrodes and the data bus line, a protection layer having contact holes, through which the common electrode line and the thin film transistor are partially exposed, respectively; depositing a transparent conductor on the protection layer; and patterning the transparent conductor to form a counter electrode including a plurality of branches arranged in parallel to the data bus line and a bar contacting the common electrode line and connecting respective one-side ends of the branches together, and a pixel electrode having a pair of first electrode parts overlapping the shields of the common electrode line while being parallel to the data bus line, second electrode parts each interposed between adjacent ones of the branches of the counter electrode, and a third electrode part connecting to respective one-side ends of the first and second electrode parts together and contacting a portion of the thin film transistor.